Optical transmitter and optical transceiver

Abstract

An optical transmitter includes a driver amplifier, a superimpose, an optical modulator, a detector and a controller. The driver amplifier amplifies a high-frequency signal. The addition processor adds a dither signal to the high-frequency signal amplified by the driver amplifier. The optical modulator modulates an optical signal according to the high-frequency signal to which the dither signal is added. The detector detects a fluctuation level of the dither signal from the modulated optical signal. The controller controls a gain of the driver amplifier that amplifies the high-frequency signal so that an output amplitude of the driver amplifier is constant based on the detected fluctuation level of the dither signal.

What is claimed is: 
     
         1 . An optical transmitter comprising:
 a driver amplifier that amplifies a high-frequency signal;   a addition processor that adds a dither signal to the high-frequency signal amplified by the driver amplifier;   an optical modulator that modulates an optical signal according to the high-frequency signal to which the dither signal is added;   a detector that detects a fluctuation level of the dither signal from the modulated optical signal; and   a controller that controls a gain of the driver amplifier that amplifies the high-frequency signal so that an output amplitude of the driver amplifier is constant based on the detected fluctuation level of the dither signal.   
     
     
         2 . The optical transmitter according to  claim 1 , wherein the controller controls a gain of the driver amplifier so that a fluctuation level, of the dither signal, detected by the detector matches a predetermined fluctuation level set in advance. 
     
     
         3 . The optical transmitter according to  claim 1 , wherein
 the optical modulator includes:   a phase modulator that phase-modulates an optical signal according to the high-frequency signal, and   a phase adjustor that phase-adjusts the optical signal phase-modulated by the phase modulator according to a bias signal,   the addition processor includes   a second addition processor that adds a second dither signal that is the dither signal to the high-frequency signal amplified by the driver amplifier, and   a first addition processor that adds a first dither signal having a frequency same as a frequency of the second dither signal to the bias signal,   the detector detects fluctuation levels of the first dither signal and the second dither signal from the optical signal modulated by the optical modulator, and   the controller includes:   a first controller unit that controls the bias signal based on a fluctuation level of the first dither signal, and   a second controller that controls a gain of the driver amplifier based on a fluctuation level of the second dither signal after the first controller controls the bias signal.   
     
     
         4 . The optical transmitter according to  claim 3 , wherein
 the first dither signal and the second dither signal have an opposite phase correlation, and   the controller controls a gain of the driver amplifier so that the first dither signal and the second dither signal are canceled out.   
     
     
         5 . The optical transmitter according to  claim 4 , wherein the controller adjusts a fluctuation level, of the second dither signal, detected by the detector according to a fluctuation ratio between a fluctuation level, of the first dither signal, detected by the detector and an initial fluctuation level set in advance, and controls a gain of the driver amplifier so that the adjusted fluctuation level of the second dither signal and the fluctuation level, of the first dither signal, detected by the detector are canceled out. 
     
     
         6 . An optical transceiver comprising:
 an optical transmitter that outputs transmission light using an electrical signal and an optical signal according to transmission data; an optical receiver that receives reception light using the optical signal and obtains an electrical signal according to reception data from the received reception light; and a processor that executes a signal process on the electrical signal, wherein   the optical transmitter includes   a driver amplifier that amplifies a high-frequency signal,   a addition processor that adds a dither signal to the high-frequency signal amplified by the driver amplifier,   an optical modulator that modulates an optical signal according to the high-frequency signal to which the dither signal is added,   a detector that detects a fluctuation level of the dither signal from the modulated optical signal, and   a controller that controls a gain of the driver amplifier that amplifies the high-frequency signal so that an output amplitude of the driver amplifier is constant based on the detected fluctuation level of the dither signal.